It is known to mold polyethylene and polyethylene compositions into variously shaped articles, such as films and bottles, using molding techniques, such as injection molding, blow-molding, and extrusion molding. In packaging industries, there is a desire to use bottles and other containers having a glossy appearance. Apart from a glossy appearance, such a container should also have certain mechanical and chemical properties. For use in a blow-molding technique, often a high density polyethylene is used in view of the desired rigidity of the container. These high density polyethylenes (HDPE), however, have poor gloss properties. Therefore, typically an HDPE is coextruded with a free radical polymerized low density polyethylene (LDPE) as an outer layer to provide a container having both rigidity and good gloss properties. Such coextruded containers, apart from requiring more complicated equipment and production processes, have a poor scratch resistance due to the low density of the outer LDPE layer. Further, the use of specific processing aids with gloss improving characteristics have been proposed, such as processing aids of the fluorocarbon elastomer or organosilicone type. These specific processing aids are, however, relatively expensive and frequently require lengthy pre-conditioning of the processing equipment.
Japanese Published Patent Application 64-87226 (Mar. 31, 1989) describes a method for manufacturing hollow molded articles using a die of which part (including the tip) or all of the inner surface is made from a fluorine resin molding and a composition consisting of 30 to 90 weight percent of high density polyethylene of a density of at least 0.946 g/cm.sup.3 and a melt index of 0.01 to 3.0 g/10 min, and 70 to 10 weight percent of a straight chain low or medium density polyethylene having a density of 0.910 to 0.940 g/cm.sup.3, a melt index of 0.1 to 10.0 g/10 min, and a polydispersity (M.sub.w /M.sub.n) of 6.0 or less. According to the examples and comparative examples of this reference, a blend is used of 70 weight percent high density component of density 0.955 g/cm.sup.3 and melt index 0.3 g/10 min and 30 weight percent of linear low density polyethylene having a density of 0.925 g/cm.sup.3, a melt index of 0.7 g/10 min, and a polydispersity of 5.0. A good surface gloss was only obtained with such a blend when the die was coated with fluorine containing resin.
Japanese Published Patent Application 03-115341 (May 16, 1991) describes a container having an outer surface consisting of 25 to 75 weight percent of LLDPE with a melt index of 1.0 to 3.0 g/10 min and a density of up to 0.935 g/cm.sup.3, with 75 to 25 weight percent of an HDPE with a melt index of 0.1 to 1.5 g/10 min and a density of at least 0.942 g/cm.sup.3. In an example, a composition of 25 weight percent LLDPE having a melt index of 2.1 g/10 min and a density of 0.935 g/cm.sup.3, and 75 weight percent of an HDPE of melt index 0.4 g/10 min and a density of 0.958 g/cm.sup.3 is extrusion blow-molded to obtain a bottle having improved gloss and increased coefficients of static and dynamic friction compared to bottles produced from HDPE alone.
Japanese Published Patent Application 05-310241 (Nov. 22, 1993) describes polyethylene resin hollow molded containers wherein a polyethylene composition with a melt index of 1.0 to 10 g/10 min consisting of 95 to 20 weight percent of an ethylene homopolymer or ethylene/.alpha.-olefin interpolymer with a melt index of 0.1 to 3.0 g/10 min, a density of 0.940 or more, and a polydispersity of 5 to 20, and 5 to 80 weight percent of ethylene/.alpha.-olefin interpolymer with a melt index of 3.0 to 50 g/10 min and a density of 0.935 or less, is used for at least the outer surface layer for the molded container. The preferred compositions have a melt index of 2.0 to 6.0 g/10 min and contain 80 to 30 weight percent of high density component having a melt index of 0.1 to 2.0 g/10 min, a density of 0.945 to 0.970, and a polydispersity of 5.5 to 15, and 20 to 70 weight percent of low density component having a melt index of 3.0 to 30 g/10 min and a density of 0.900 to 0.930. The examples and comparative examples show that a low density component having a melt index less than 3.0 gives a poor gloss value.
The present invention relates to compositions that can be molded into articles having an improved gloss and impact strength while maintaining adequate rigidity levels, when compared to state-of-the-art HDPE molding compositions. The present invention further relates to compositions that can be molded into articles with essentially the same equipment as used for molding state-of-the-art HDPE compositions, without requiring specific coatings on the die and without requiring the use of more expensive processing aids of the fluorocarbon elastomer or organosilicone type.